Objectives: 1. know the characteristics of the jawless fishes2. compare and contrast between reproductive modes of sharks3. identify a variety of sensory adaptations of cartilaginous fishes.4. differentiate between skates and rays

Jawless fishes

• Lack both jaws and paired appendages.• Bodies are entirely composed of cartilage, no

bone.

Hagfish

Hagfish

• Hagfish: “slime eels” bottom-dwelling fish usually found in deep oceans.

• Use a dental plate to grasp the flesh of their prey tearing away bites.

• Many are scavengers.• Because hagfish cannot penetrate the skin of

whales or fish, then enter the body cavity through the mouth or anus and eat the carcass from the inside out.

Cartilaginous Fishes(Chondrichthyes)

SharksSkatesRays

Chimaeras

Characteristics of Cartilaginous fishes

• Their skeletons are composes entirely of Cartilage often strengthened by the deposit of calcium salts.

• Possess jaws and paired fins.• Placoid scales: sandpaper like covering on

sharks, and spines on the back of skates and rays.

Sharks

• Streamlined bodies. Use their massive trunk muscles in sideways sweeps of the caudal fin, or tail.

Shark sensory system

• Vision seems to be of less importance than olfaction (smell) in finding prey.

• 2/3 of the brain cells are used in processing olfactory information. “swimming noses”

Sensory system: The lateral line

• Consists of canals running the length of the body at regular intervals.

• The canals open for free movement of water in and out, where sensory receptors detect vibrations in the fluid filled canals.

Sensory system: Ampullae of Lorenzini

• Allows for the sense of electrical currents in the water.

• Can sense charges as little as a tenth of a microvolt.

• Sensitive enough to detect the electrical fields created by muscle movements of their prey.

Reproduction in Sharks

• Oviparity: the most primitive mode: eggs are laid outside the body and the embryos develop in a protective case.

• Ovoviviparity: the most common method is sharks. Eggs hatch within the mother’s uterus, but no placental connection is made.

• Viviparity: young directly attach to mother’s uterine wall, or uterine milk is produced that is absorbed by the embryo.

• Requeim and hammerhead.

Skates and Rays

• Skates swim by moving their fins up and down, like a bird flies. Rays create a wave like motion with their fins.

• The tails of rays are streamlined and contain venomous spines. Skates do not.

Chimaeras

• Relatives of the sharks, that have large pinted heads and long slender tails.

• Unlike other cartilaginous fishes the gills are covered with an operculum, and water is taken in through the nostrils.